In recent years, researches are being made of a quantum computer which performs a computation by using quantum-mechanical superposition. As one of quantum computers, a quantum computer based on frequency domain quantum computation that discriminates between qubits (quantum bits) in frequency domains is known in the art. In the frequency domain quantum computation, qubits are not discriminated in terms of their positions. Therefore, even qubits that are not to be manipulated are under the effect of operation light with detuning, causing undesired interaction. The undesired interaction may cause gate errors. The adverse effects caused by the undesired interaction may decrease if the frequency difference of the transitions used for qubits is very large. Where the transition distributed in a finite frequency domain is used, however, transitions of small frequency differences may have to be used to load a large number of qubits. Even where the transitions of small frequency differences are used, a quantum computer required is a computer based on the frequency domain quantum computation capable of performing a quantum gate while suppressing the effects caused by the undesired interaction.